If I remember correctly it is Spain
The answer to choose: A) Carter was instrumental in negotiating the Camp David Accords, which directly led to the 1979 Egypt-Israeli Peace Treaty.
Details:
Thanks to the persistent efforts of President Carter in working with Egyptian President Anwar Sadat and Israeli Prime Minister Menachem Begin, those two leaers signed the Camp David Accords in September, 1978. That led to the 1979 peace treaty between Egypt and Israel that has lasted to the present day. Sadat and Begin were awarded the Nobel Peace Prize in 1978 for their efforts in reaching the agreement that they made.
As to the other answers:
The fact that Carter allowed the deposed shah of Iran to come into the USA for medical treatment did provoke the hostage seizure in Tehran. However, that was not a major <u>success</u> of Carter's foreign policy, but a major mistake. (His advisors had tried to tell him in advance that letting the shah come into the US was a bad idea.)
Similarly, the increase of tensions with the Soviet Union over the Olympics would not be an example of a success.
The federal law regarding cleaning up hazardous waste would be a success item, but one of <u>domestic</u> policy, not foreign policy.
